This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from my application OPTICAL ADD-DROP MULTIPLEXER AND WAVELENGTH DIVISION MULTIPLEXING OPTICAL LINK USING THE SAME filed with the Korean Industrial Property Office on Aug. 4, 1998 and there duly assigned Serial No. 31701/1998.
1. Field of the Invention
The present invention relates to an optical add-drop multiplexing technique and a wavelength division multiplexing (WDM) optical link including such a multiplexing technique, and more particularly, to an optical add-drop multiplexer (OADM) for adding and dropping wavelength groups among multiplexed and input wavelength groups for each of a plurality of nodes, and a WDM optical link including such a multiplexer.
2. Description of the Related Art
Earlier WDM optical links using an OADM selectively drop wavelengths to each of a plurality of nodes (dropped channels), and pass the other wavelengths (pass channels). The optical signals of dropped channels are transmitted to the local areas covered by a node for each of the channels. Also, the optical signals transmitted from the local areas are supplied to an optical receiver which converts them into electrical signals. The electrical signals which are included in some new data are converted into optical signals having the same wavelengths as those of the dropped channels and then added to the pass channels by an optical multiplexer. The nodes output optical signals which have the same number of channels as the number of channels input thereto and the same wavelengths as those of the input channels.
Such an OADM includes a wavelength division demultiplexer (DMUX) for demultiplexing and a wavelength division multiplexer (MUX) for multiplexing. The OADM operates as follows. If sixteen channel wavelengths are multiplexed and input to the DMUX, the DMUX demultiplexes sixteen channels and drops four channels to be transmitted to the local areas covered and allows the other channels to pass therethrough. The MUX multiplexes the four channels input from the local areas and the pass channels.
When such an OADM is used, one or more new wavelengths are provided to a node in response to a request from the node. An apparatus required for wavelength extension in the abovenoted OADM includes a 2-channel separator, a first DMUX, a first MUX, a second DMUX, a second MUX, and a 2-channel coupler. The first DMUX and the first MUX drop and add respectively four channels among sixteen channels for a node. In the case of extending channels for the node, the 2-channel separator, the second DMUX, the second MUX, and the 2-channel coupler must be further provided. In other words, the 2-channel separator separates the input channels into a group of sixteen channels in use and another group of channels including the channels to be extended. The second DMUX and the second MUX drop and add respectively the channels to be extended from and to the other group of channels. The 2-channel coupler couples the group of sixteen channels and the other group of channels and transmits them to the next node.
However, the OADM discussed above requires an additional DMUX and MUX for securing the capacity of new channels and extending wavelengths. To this end, it is necessary to acquire a system operators"" permission. Service providers can use the channels only when the system operators hand over the channels to them. Thus, channel capacity and wavelength extension is a costly and time-consuming work.
To solve the above problems, it is an object of the present invention is to provide an optical add-drop multiplexer (OADM) for binding wavelengths required by each node into one wavelength group, dropping the wavelength group from the multiplexed input wavelength groups, selecting channels from the wavelength group and adding the wavelength group to the wavelength groups, and a WDM optical link having such an OADM.
Accordingly, to achieve the above object, there is provided an OADM for dropping channels for a predetermined area covered by an optical node and adding input channels from the area to be transmitted to a next optical node, the OADM including: a wavelength group demultiplexer for separating a plurality of input channels into groups of channels and dropping a channel group required for the node and passing the other groups of channels therethrough; a channel selector for selecting channels from the wavelength group output from the wavelength group demultiplexer and transmitting the selected channels to the area; a channel multiplexer for multiplexing the channels having the same wavelengths as those of the selected channels and input from the area into the wavelength group, and a wavelength group multiplexer for adding the wavelength group input from the channel multiplexer to the wavelength groups that have passed through the wavelength group demultiplexer.
According to another aspect of the present invention, there is provided a wavelength division multiplexing (WDM) optical link having a plurality of optical nodes connected to each other through optical fibers, each node including an optical add-drop multiplexer (OADM) for dropping channels required for a predetermined area covered by each node and adding input channels from the area to be transmitted to a next optical node, wherein the OADM includes: a wavelength group demultiplexer for separating a plurality of input channels into groups of channels and dropping a channel group required for the node and passing the other group of channels therethrough; a channel selector for selecting channels from the wavelength group output from the wavelength group demultiplexer and transmitting the selected channels to the area; a channel multiplexer for multiplexing the channels having the same wavelengths as those of the selected channels and input from the area into the wavelength group, and a wavelength group multiplexer for adding the wavelength groups input from the channel multiplexer to the wavelength groups that have passed through the wavelength group demultiplexer.